Chemical-reaction equation {chemical equation} uses molecule chemical formulas and special symbols. Reactant formulas are on left, and product formulas are on right.
direction
Horizontal arrow pointing right separates reactants from products. Delta symbol means to add heat. hv symbol means to add light.
terms
Plus signs separate molecules.
symbols
Up arrow (^) at formula right indicates that reaction produces gas. Down arrow at formula right indicates that reaction precipitates solid. The letter s at formula right means that reagent is solid. The letter l at formula right means that reagent is liquid. The letter g at formula right means that reagent is gas. The letters aq at formula right mean that reagent is aqueous.
balance
Atoms on chemical-reaction left must also be on right, so both sides have same atom numbers and types {conservation of mass, chemical equation}.
Before chemical reaction, chemicals {reactant}| {reagent} exist.
If chemical reaction has more than one reactant, one reactant {limiting reagent}| depletes first as reaction proceeds. Find limiting reagent from balanced chemical reaction, using the following rule. If first-reactant coefficient to second-reactant coefficient ratio is larger than first-reactant moles to second-reactant moles ratio, second reactant is limiting reagent.
After chemical reaction, new chemicals {product, reaction}| exist.
Relative reactant and product masses have relations {stoichiometry}|.
If written chemical reaction has one product or reactant missing, calculations {balancing chemical equation} can find missing product or reactant. If written chemical reaction has one coefficient missing, calculations can find missing coefficient.
First, find all missing atoms, because each atom on left must also be on right.
Using found atoms, write positively charged atom symbol first and negatively charged atom symbol second.
Use naming-formula rules to find candidate molecule, using number subscripts for symbols if necessary.
Write equation using candidate molecule.
Add coefficients to reactants and products to make atom numbers equal on both sides. To find coefficients, first balance metal-atom coefficients, then balance non-metal-atom coefficients, except H and O, then balance hydrogen coefficients, and finally balance oxygen coefficients. If chemical equation is not yet balanced, double metal-atom coefficients, then balance non-metal-atom coefficients, except H and O, then balance hydrogen coefficients, and finally balance oxygen coefficients.
In chemical reactions, total mass {conservation of mass, reaction}, total charge {conservation of charge}, and total energy {conservation of energy, reaction} stay constant. Sum of reactant charges equals sum of product charges. Total reactant mass equals total product mass. Reactant energy equals product energy plus heat.
In chemical reactions, formed or used gas volumes relate by whole-number ratios {combining volumes law} {law of combining volumes} {Guy-Lussac law} {law of Guy-Lussac}.
In reaction series, in which previous-reaction products are next-reaction reactants, total change over series equals sum of reaction changes {Hess' law} {Hess law}.
Chemical-reaction product amount {yield, reaction}| never equals maximum theoretical product amount, because reactions are inefficient. Calculating reaction efficiency {percent yield} uses the balanced chemical reaction. Percent yield equals ratio between product moles and limiting-reagent moles, expressed as percentage.
Knowing chemical equation and reactant and product concentrations at equilibrium allows reaction-constant calculation {equilibrium constant}|. Equilibrium constant is product of product concentrations, each raised to power of its chemical-equation coefficient, divided by product of reactant concentrations, each raised to power of its chemical-equation coefficient. For example, in chemical equation 2 A + 3 B -> C + 4 D, equilibrium constant K = ([A]^2 * [B]^3) / ([C] * [D]^4). Chemical reaction aX + bY -> cZ + dW equilibrium constant is K = (X^a * Y^b) / (Z^c * W^d).
tables
People know many reaction equilibrium constants, at specific temperatures. Dissociating acids and bases have equilibrium dissociation constants. Dissolving salt in water or other solvent has equilibrium solubility constant.
irreversible
Equilibrium constant greater than 10^9 means reaction is irreversible.
product concentrations
Equilibrium constant and initial reactant concentrations result in product concentration at equilibrium. First, use chemical equation to make equilibrium-constant equation with correct exponents. In equilibrium-constant equation, replace product concentration with x if coefficient is 1, replace with 2*x if coefficient is 2, replace with 3*x if coefficient is 3, and so on. If coefficient is 1, replace reactant concentration with its initial concentration minus x. Replace with 2 * (initial concentration minus x) if coefficient is 2. Replace with 3 * (initial concentration minus x) if coefficient is 3, and so on. For example, for chemical equation 2 A + 3 B -> C + 4 D, equilibrium constant K = ([A]^2 * [B]^3) / ([C] * [D]^4). To find A concentration: K = ((2*x)^2 * B^3) / (C * D^4). Use equilibrium constant value from table of constants. Solve for x.
Product concentration is x times its coefficient in chemical equation. Reactant concentration is (initial concentration minus x) times its coefficient in chemical equation.
partition functions
Reactant and product partition functions can find chemical-reaction equilibrium constant.
After reaction, reactant and product amounts stay constant {equilibrium, reaction}|. At equilibrium, total-energy change is zero, free-energy change is zero, substance change is zero, all chemical potentials are equal, and all forces are equal. Product concentrations and reactant concentrations have equilibrium-constant ratio.
rates
At equilibrium, forward and backward reaction rates are equal. Product-formation rate equals reactant-formation rate. Amounts do not change, so reaction is complete.
factors
Equilibrium concentrations and amounts do not depend on catalyst or factors affecting reaction rate. Equilibrium concentrations depend only on energies and entropies.
factors: temperature
If reaction requires heat, temperature increase makes more product.
factors: pressure
If gas is reactant, pressure increase makes more product. If temperature increases, system acts to reduce pressure and so return to equilibrium.
factors: amount
Adding more reactants changes them to products, until equilibrium reestablishes. Adding more products turns them into reactants, until equilibrium reestablishes. Increasing reactant concentration, or removing product, increases product.
5-Chemistry-Inorganic-Chemical Reaction
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Date Modified: 2022.0225